This invention relates to printheads for ink jet printing apparatus, and more particularly to a printhead of this class having a plurality of jet orifices arranged in a matrix for discharging droplets of ink to print data on a surface moving past the printhead.
In certain respects, the invention involves improvements on the printhead disclosed in the coassigned U.S. Pat. No. 4,723,131 of Jimmy L. Droit, issued Feb. 2, 1988, which is incorporated herein by reference.
Reference may also be made to the coassigned U.S. Pat. No. 4,792,817 issued Dec. 20, 1988 for a disclosure of a printhead on which, in certain respects, the invention of said U.S. Pat. No. 4,723,131 is an improvement, and on which the present invention may be regarded as involving improvements.
Reference may also be made, as in said U.S. Pat. No. 4,723,131, to U.S. Pat. Nos. 4,215,350, 4,378,564, 4,542,386, 4,450,375, 4,555,719 and 4,576,111 for their disclosures of printheads of this class.
While the printhead disclosed in said U.S. Pat. No. 4,723,131 has been quite satisfactory for many purposes, including as stated therein the printing of relatively small characters (e.g., alphanumeric characters), it has been found that spacing of its orifices cannot be reduced for printing even smaller characters such as may be desired, the reduction of the spacing of the orifices being limited in the case of the use (as has been found desirable) of the heads or pistons designated 202 in said patent by the diameter required for these members. Thus, for example, it has been found impractical to space the orifices any closer than 0.050", characters printed with this spacing being of the order of 5/16" high. Also, the printhead disclosed in said U.S. Pat. No. 4,723,131 includes an insert designated 52 in said patent which has been found not only to add to the cost of the printhead (including assembly cost) but also adversely to affect the consistency of the printing in some instances. Further, consideration was given to utilizing the principles of the printhead disclosed in said U.S. Pat. No. 4,723,131 for printing bar codes, but it was found difficult to obtain sufficient flow of ink for such printing.